1. Field of the Invention
The present invention relates to a method for sealing areas in a well bore, and more particularly, by not by way of limitation, to an improved method for inserting a tubular viscoelastic material into a casing affixed within a well bore for repairing breaches in the casing.
2. Description of Related Art
As the drilling of an oil or gas well progresses, the well bore is lined with a casing that is secured in place by a cement slurry injected between the exterior of the casing and the well bore. The casing functions to provide a permanent well bore of known diameter through which drilling, production or injection operations may be conducted. The casing also provides the structure for attaching surface equipment required to control and produce fluids from the well bore or for injecting fluids therein. In addition, the casing prevents the migration of fluids between subterranean formations through the well bore, i.e., the intrusion of water into oil or gas formations or the pollution of fresh water by oil, gas or salt water.
The mechanical integrity of the casing and the ability of the casing to isolate subterranean formations is closely regulated. Casing which has been cemented in a well bore is required to pass a mechanical integrity test to assure that no breaches in the casing occur. If the casing fails the mechanical integrity test, the casing must be repaired. Mechanical integrity failure can result from various means, such as corrosion, old perforations, or other breaches in the casing including joint leaks, split casing or parted casing.
Mechanical integrity failures are normally repaired by either replacing the defective casing, cementing a new casing inside the old casing, or injecting cement into the breach of the casing which is commonly known as "squeeze cementing". Replacement of defective casing is often not feasible because of the initial completion method used and the risk in damaging additional casing due to stress imparted on the casing during such an operation. Because the operation of inserting a new casing inside the old casing is expensive, this option may not be economically feasible. Additionally, squeeze cementing is not always economically feasible, and is inappropriate for certain types of subterranean formations. Furthermore, when squeeze cementing is utilized, satisfactory results are not always obtained. Finally, each of these remedies are costly in terms of the amount of time required for each operation, and therefore, the amount of time that the well is out of service.
To avoid the expense and time associated with the above-mentioned remedies, sealing apparatuses employing retrievable packers have been utilized for sealing and isolating casing at the point of the mechanical integrity failure. However, when employing such sealing apparatus, problems have been encountered. For example, the annular flow of fluids about a tubing string which extends through the sealing apparatus is often restricted, thus producing a hydraulic breaking effect as the apparatus is inserted into the well bore. Further, the annular flow may be restricted during mechanical integrity testing which requires an annulus between the tubing string and the casing. Lastly, the sealing apparatus is often ineffective because the resilient sealing elements become worn or deteriorate due to rough or, cement-coated interior casing walls when the sealing apparatus is inserted into the well bore.
A method of lining the casing with a continuous string of tubular viscoelastic material has also previously been proposed. This method is disclosed in U.S. Pat. No. 5,454,419, issued to Jack Vloedman, the present inventor. The method disclosed in the Vloedman '419 patent utilizes a continuous, seamless viscoelastic tubular liner wound on a portable spool. The liner, which has an outer diameter greater than the inner diameter of the casing, is reeled off the spool and through a roller reduction unit to reduce the diameter of the liner so that the liner can be injected into the casing. A weight system connected to the bottom end of the liner maintains the reduced liner in tension so that the liner remains in its reduced state until the liner is positioned at a desired depth. After the liner is run to such depth, the weights are removed thereby allowing the reduced liner to rebound and form a fluid tight seal with the casing and effectively sealing any breaches in the casing.
While the method disclosed in the Vloedman '419 patent has successfully met the need for repairing breaches in casing in an effective and time efficient manner, several inefficiencies have nevertheless been encountered, particularly in circumstances when only a selected segment of the casing is in need of repair. That is, if only a relatively short section of approximately 100 to 2000 feet of casing is in need of repair and this section is located several thousand feet below the surface, for example, it is more cost effective if the casing does not have to be lined entirely from the surface to the pertinent section. In addition, viscoelastic tubing has less tensile strength than conventional steel tubing. As such, in attempting to line the casing at depths below about 5,000 feet, the weight of the weight system coupled with the weight of the lining run into the casing can cause the lining to fatigue or even fail.
To this end, a need exists for an improved method for patching selected sections of casing with segments of viscoelastic tubing having a length less than the distance extending between the surface and a preselected depth to repair breaches therein which is durable and effective, while remaining inexpensive and time efficient. It is to such an improved method that the present invention is directed.